Tillage disc



April 5, 1955 J. H. INGERSOLL 2,705,448

TILLAGE DISC Original Filed July 10, 1951 3 Sheets-Sheet l [RUE/72 5f"James ff [@ersoll April 5, 1955 J. H. INGERSOLL 2,705,448

TILLAGE msc Original Filed July 10, 195i 5 Sheets-Sheet 2 fnz/eni ar'"22 Jams ff [T ger-sell April 5, 1955 J. H. INGERSOLL TILLAGE DISC 3Sheets-Sheet 3 Original Filed July 10 1951 C/earance be/a/een Punch andDie- [fir/safar James I]: fqgens'oll United States Patent TILLAGE DISCJames H. Ingersoll, Flossmoor, Ill., assignor to Borg- IXarnerCorporation, Chicago, Ill., a corporation of Original application July10, 1951, Serial No. 236,004. gigiggtsl and this application July 10,1951, Serial No.

6 Claims. (Cl. 97-217) The present invention relates in its broadestaspects to sheet metal articles and more specifically to an improvedhigh carbon steel earth cutting disc particularly applicable toagricultural implements and the machine or fixture and method for makingsuch a disc with spaced peripheral recesses defined by surfaces whichconverge with one side of the disc to provide sharp cutting edges.

Although the present application fully discloses the fixture and methodfor making the new and improved earth cutting disc, only the disc per seis claimed herein, the disclosure of the fixture and method for makingthe disc being deemed to facilitate a complete and thoroughunderstanding of the new and improved disc. The fixture and method formaking the disc are disclosed and claimed in my copending application,Serial No. 236,004, filed July 10, 1951, the present application being adivision of the last-mentioned application which covers the fixture andmethod for making the disc.

For a considerable period of time it has been a rather common practiceto utilize implements, for agricultural and other types of earth workingand cutting purposes, comprising steel discs for breaking up and workingthe earth, which, when the implement is being used for agriculturalpurposes is very etfective in rendering the soil more suitable forplanting. In such implements it is customary, in at least one typethereof, to arrange a plurality of the discs upon a common axis suchthat the complete implement may be pulled over the earth with the axisof the discs positioned at an angle somewhat less than 90 from the lineof forward movement of the implement. The discs are somewhat concave andwhen the implement is used in this manner the individual discs, althoughtending to roll to a certain extent, also cut or dig into the soilthereby turning it over and breaking it up as is particularly necessarybefore a crop may be planted. More recently an improved form of suchimplements has utilized discs that are provided with notches aroundtheir peripheries. The periphery of each individual disc in theseimproved implements is tapered slightly in order to facilitate theentrance of the disc into the soil and the periphery of the individualnotches in each of the discs is sharpened in order to further facilitatethe cutting and working up of the earth. Such an improved earth workingimplement has been found to be very effective as a device forconditioning the earth prior to planting a crop therein or prior to anengineering operation requiring the removal of a layer of earth.

The notched discs utilized in the improved type of earth cuttingimplement referred to briefly in the preceding paragraph have quitegenerally been manufactured in a rather uneconomical manner, asheretofore the notches have been punched by a punch that passes throughthe disc periphery, travelling through a path substantially normal tothe sides of the disc, thereby leaving a land for each notch which mustbe ground off to provide the cutting edge. Quite generally the frictionduring the grinding operation necessary to remove the land and producethe cutting edge for each notch heats the portions of the discsurrounding the notch to such an extent that the metallurgicalcharacteristics of the metal surrounding the notch are considerablychanged. As is well known, it frequently happens, during the grindingoperation, that the temperature of the disc in the vicinity of the notchperiphery increases to a value above the critical point for the materialof which the disc is made and as a result the temper of the disc aroundthe notch periphery is withdrawn. Subsequently, the disc, which is2,705,448 Patented Apr. 5, 1955 punched and ground under normalatmospheric conditions, becomes air cooled. During this air cooling ofthe portion of the disc subjected to heating by the grinding operationthe temper is restored but it has been found that in at least a ratherhigh percentage of cases unstable martensitic steel is formed on thesharp edge bounding the notch or recess. As is well known, this unstablemartensitic steel is very hard and brittle and is particularly subjectto surface cracking.

Due to the fact that the grinding period is not absolutely definite, andbecause the notch peripheries are heated to different temperatures andsince the temperature ofthe notch peripheries is a function of thethickness of the metal in contact with the grinding wheel, there isusually a temperature gradient from a high value at the sharpest pointof the notch periphery toward the center of the disc. As a result ofthis temperature gradient, the subsequent cooling, due to what might becalled, air quenching, causes a gradient in the hardness of the: cuttingedges, which is present in a very high percentage of the earth cuttingdiscs that are notched in the conventional manner.

Earth cutting discs manufactured in the conventional manner wherein thenotch peripheries are ground after being punched in order to providesharp cutting edges for each notch, have been found in many instances,when the discs are actually put to use, to be inferior. As has beenpointed out heretofore, the subsequent air cooling after the grindingoperation often may cause unstable martensitic steel to be formed at thecutting edges and also it is not uncommon for some of the cutting edgesto comprise a steel that is softer than the remaining portions of thedisc. If the cutting edges are harder than the other portions of thedisc they are more brittle and far more subject to breaking when thedisc strikes a relatively heavy object. Such a break very often extendsgenerally radially inwardly of the disc several. inches in the form of acrack and, as is obvious, such a crack severely weakens the disc. Whenthe cutting edges are softer than the remaining portions of the discthey tend to become dull and wear away rapidly, which is alsounsatisfactory. When the cutting edges are of substantially the samehardness as the rest of the disc the cracking of the disc in a generallyradial or chordal direction is considerably lessened and a much moresatisfactory and longer wearing earth-cutting disc is thereby provided.

The principal object of the present invention is therefore to provide anearth-cutting disc, having a notched periphery, wherein each of thenotches is defined by a surface that converges with one side of the discto provide a cutting edge and wherein the disc is made of a steel ofsubstantially the same hardness throughout.

Another important object of the invention is to provide a hard steelearth-cutting disc having a scalloped cutting edge formed by merelyshearing a plurality of recesses in the disc periphery at an acute anglewith respect to the sides of the disc, thereby eliminating the grindingoperation necessary to provide the cutting edge for each of the recessesin discs made by conventional methods.

Another object of the present invention is to provide an earth-cuttingdisc that is substantially circular and slightly concave, one side ofwhich is tapered slightly in the vicinity of the periphery of the discto provide a relatively blunt cutting edge around the disc periphery,and the periphery of the disc is also provided with a plurality ofuniformly spaced sheared beveled notches.

Another object of the present invention is to provide an earth-cuttingdisc which has one side that is tapered slightly around the peripherythereof, and! which has a plurality of sheared open-mouthed spacedperipheral notches, the peripheries of each of the notches intersectingone side of the disc at a variable acute angle which is sharpest at theradially deepest portion of the notch and notch formed by passing apunch through the implement in a manner such that the punch intersectsthe periphery of the implement and travels through a path making an'acute angle with the surface of the implement first engaged by thepunch to thereby provide a cutting edge for the notch.

A further object of the invention is to provide an earth-cutting dischaving a tapered peripheral portion and having a recess in theperipheral portion which is defined by a substantially generallyelliptically shaped contlnuously curved sheared surface that meets oneside of the diisc at a variable acute angle to thereby form a cutting ege.

Another object of the invention is to provide a high carbon steel earthcutting disc having opposed sides, one of which is substantiallyuniformly tapered around its periphery, and having a plurality of spacedsheared openmouthed recesses formed in the peripheral portion of thedisc, each of the recesses having a radial depth greater than the radialwidth of the taper on the one side of the disc and being defined by asubstantially continuously curved sheared surface that meets one side ofthe disc at a variable acute angle to thereby form a cutting edge foreach recess, the acute angle having its smallest value at the radiallydeepest point on the cutting edge and gradually increasing andapproaching at right angle at the ends of the curved sheared surfaceswhere they intersect the tapered disc periphery.

A further object of the invention is to provide an agricultural earthcutting disc having one side peripherally tapered to provide arelatively blunt cutting edge around the periphery of the disc andhaving a plurality of relatively sharper substantially continuouslycurved sheared recessed portions formed in its periphery, each of therecessed portions being defined by a surface that intersects the otherside of the disc at a relatively sharp acute angle in the central partof the recessed portions and at a relatively less acute angle at theends of the recessed portions so as to provide sufiicient disc thicknessat the junctures of the recessed portions and the tapered periphcry ofthe disc as will not weaken the disc at the junctures.

Another object of the invention is to provide a tempered sheet metalearth cutting disc having a peripheral portion formed with an opencontinuously curved recess therein which is defined by a pair ofintersecting compression and shear surfaces formed by passing a punchthrough the peripheral portion of the disc in a path making an acuteangle to the sides of the disc and such that the punch intersects theouter periphery of the disc, the compression surface meeting one side ofthe disc at an obtuse angle and the sheared surface meeting the otherside of the disc at a variable angle sufficiently acute to provide acutting edge.

More specifically it is an object of the present invention to provide asteel earth cutting disc having a diameter of the order of between 16and 40 inches and a thickness of the order of between A1 and /2 inch,wherein the disc periphery is scalloped by passing a punch therethroughat an acute angle to the sides of the disc to provide spaced recessedcutting edges around the disc periphery.

The above and numerous other objects and advantages of the presentinvention will become apparent from the following detailed descriptionwhen read in conjunction with the accompanying drawings, wherein:

Fig. 1 is a sectional view showing the fixture for shearing bevelednotches in the periphery of a high carbon steel earth-cutting disc;

Fig. 2 is a plan view of the fixture shown in Fig. 1;

Fig. 3 is a perspective view of the die employed in the disc notchingfixture shown in Figs. 1 and 2;

Fig. 4 is a perspective view of the punch employed in the disc notchingfixture;

Figs. 5A, 5B and 5C are fragmentary sectional views taken substantiallyalong the line 5-5 in Fig. 2 and respectively correspond to differentpositions of the punch during the notching operation;

Figs. 6A, 6B and 6C are fragmentary sectional views taken substantiallyalong the line 6-6 in Fig.2 and looking in the direction of the arrows,and also respectively correspond to different positions of the punchduring the notching operation;

Fig. 7 is a fragmentary plan view of a disc showing a notich thereinformed by the fixture disclosed in Figs. 1 an 2;

Fig. 7A is a sectional view taken substantially along the line a-a inFig. 7;

Fig. 7B is a sectional view taken substantially along the line bb inFig. 7;

Fig. 7C is a sectional view taken substantially along the line c-c inFig. 7;

Fig. 7D is a sectional view taken substantially along the line da' inFig. 7; and

Fig. 7B is a sectional view taken substantially along the line e-e inFig. 7.

Referring now to the drawings, wherein like reference numerals in thedifferent views identify identical parts throughout, and referringparticularly to Figs. 1, 2 and 7, a slightly concave, generally circularhigh carbon steel earth-cutting disc 10 is rotatably positionable in thenotching fixture, indicated generally by reference numeral 11, in orderto provide a plurality of semi-elliptical openmouthed recesses ornotches 12 in the periphery of the disc 10. The fixture 11, in general,comprises a relatively sta tionary die 13, a back-up guide member 14, areciprocable punch member 15, and an indexing mechanism I for rotat ablypositioning the disc 10 so as to bring successive peripheral portionsthereof into punching position and thereafter hold the disc in theproper position during the punching operation.

As shown particularly in Figs. 1 and 3, the die 13 comprises a block ofhard metal having one of its upper edges cut off to provide a discsupporting surface 16. As the disc 10 is slightly concave, the surface16 is slightly convex so as to be substantially complementary to theunder side of the disc 10. It will be understood, of course, that thedegree of convexity of the surface 16 depends upon the degree ofconcavity of the disc 10 and it is contemplated to be within the realmof the present invention, that when a substantially planar disc is beingnotched, the disc supporting surface 16 will also be substantiallyplanar so as to be complementary to such a disc.

The die 13 is also provided with a punch guiding surface 17 which issubstantially semi-cylindrical and which intersects the disc supportingsurface 16 to provide a combined shearing, back-up and compression edge18 on the die 13. The combined shearing, back-up and compression edge18, being defined by the line of intersection between the punch guidingsurface 17 and the disc supporting surface 16, comprises a continuouslycurved edge having a substantially semi-elliptical shape. The edge 18varies from a true ellipse only because of the convex character of thesurface 16. As will be brought out more fully hereinafter, the shape ofthe edge 18 is critical in that it is important that it makes linecontact with the under surface of the disc 10 at all points throughoutthe length of the edge 18. However, it is not critical that the rest ofthe surface 16 engage the under surface of the disc 10 at all points onthe surface, it being sufiicient that the surface 16 substantiallyconform to the under surface of disc 10, so as to firmly support thedisc.

The punch 15 comprises a block of hard metal formed with a cylindricalsurface 19 substantially complementary to the cylindrical punch guidingsurface 17 formed on the die 13. The radius of curvature of thecylindrical surface 19 on the punch 15 is, however, sufficiently smallerthan the radius of curvature of the surface 17 on the die 13 to providethe necessary clearance between the punch 15 and the die 13 when thepunch is moved downwardly into the die. As is best shown in Figs. 7 and7A the upper surface of the disc 10 is slightly tapered, as at 20, andthe cylindrical portion 19 of the punch 15 is cut oif so that the lowersurface of the punch is substantially complementary to the peripheralportion of the disc 10 when the punch 15 is moved into engagement withthe disc. Since the punch 15 is cut off in this manner, two surfaces 21and 22 are provided on the lower end of the punch 15, the surface 21being substantially complementary to the upper surface of the disc andthe surface 22 being substantially complementary to the taperedperipheral surface 20 of the disc 10. The two surfaces 21 and 22 bothintersect the cylindrical surface 19 of the punch 15 to provide acombined compression and shearing edge 23 for line contacting the uppersurface of the disc 10 when the punch 15 is moved into engagementtherewith. The compression and shearing edge 23 is composed of one part23a formed by the intersection of the surfaces 21 and 19, and of twoparts 23b formed by the two intersections between the surfaces 22 and19. As will also appear hereinafter, it is important that the combinedcompression and shearing edge 23 makes line contact with the uppersurface of the disc 10 at all points throughout its length when thepunch 15 is moved into engagement with the disc, however, it is notcritical whether the remaining portions of the surfaces 21 and 22 be anymore accurately formed than is suflicient to provide substantialengagement with the upper surface of the disc throughout these surfaces.

The back-up reaction guide member 14, as well as the die 13, is suitablybolted to a main base plate 24. The guide member 14 is cut out so as toprovide a guiding surface 25 that is complementary to the punch 15 andserves to back-up the punch 15 upon movement thereof downwardly throughthe disc 10. The internal dimensions of the guiding surface 25 arelarger than the external dimensions of the punch 15 by an amountsufficient only to permit free sliding movement of the punch in theguiding member 14. It is not necessary that there be any great amount ofclearance between the punch 15 and the back-up member 14 because, infact, the punch 15 is urged against the back-up member 14 duringmovement of the punch downwardly through the disc 10 by a ratherconsiderable force, the guide member 14 serving at this time as areaction member.

Also bolted to the base plate 24 is a pair of disc positioning members26 and 27, each of which is provided with a surface 28 that issubstantially complementary to the upper surface of the disc 10 andwhich, in conjunction with the disc supporting surface 16 on the die 13,serves to maintain the peripheral portion of the disc 10 in a verticallystationary position.

The indexing mechanism I for angularly positioning the disc 10 about itsown axis, indicated by the dotted line 29, is mounted upon a block 30rigidly bolted to the base plate 24. The block 30 has an upper beveledsurface 31 and has a cylindrical opening 32 that extends through thebeveled surface 31 in a direction substantially perpendicular to thebeveled surface 31. Rotatably positioned within the opening 32 is acylindrical sleeve 33 which is provided with an annular groove 34 forreceiving a stud 35 which retains the sleeve 33 in the proper verticalposition. The sleeve 33 is internally threaded and receives a discsupporting member 36 which has mating external threads engageable by theinternal threads on the sleeve 33. A lock nut 37 is also threaded ontothe threaded portion of the disc supporting member 36 for the purpose ofrigidly clamping together the disc supporting member 36 and the sleeve33. The member 36 is internally bored and threaded, as indicated at 38,for the purpose of receiving a disc locating bolt 39. The bolt 39 has acentral shoulder 40 for seating the disc 10 and is externally threaded,as at 41, on its upper portion. A collar-like member 42 is internallythreaded to mate with the threads 41 in order to clamp the disc 10against the supporting member 36. When the lock-nut 37 is screwed downagainst the sleeve 33 and the collar 42 is screwed down against the disc10, all of these members comprise a single rotatable unit. Means areprovided for holding the disc 10, supporting member 36 and sleeve 33stationary in any desired angular position so as to bring successiveperipheral port1ons of the disc 10 into a position to be notched by thepunch 15 and die 13. Such means will now be described. A block 43 issecured to the block 30 and is formed with a track 44 having overhanginglips 45 for receiving and holding a latch 46 therein. The latch 46 isslidable in the track 44 and has a tooth 47 which is movable into anyone of a plurality of slots 48 formed around the periphery of a flange49 on the sleeve 33. When the tooth 47 is seated within one of the slots48, the sleeve 33, supporting member 36 and disc 10 are held fixedangularly about the axis 29 of the disc 10. A block 50 is secured to theblock 11 and pivotally supports a manually movable lever 51. The lever51 is provided with a slot 52 and a pin 53, secured to the latch 46,extends through the slot 52. A tension spring 54, secured at one end tothe lever 51 and secured at its other end to the block 30 biases thelatch 46 into the position shown in Fig. 2, wherein the tooth 47 isseated within one of the slots 48 formed in the flange 49. Upon themanual movement of the lever 51 in a clockwise direction (see Fig. 2)the latch 46 is withdrawn so that the disc 10, supporting member 36 andsleeve 33 may be rotated until the next successive notch 48 is oppositethe tooth 47. The tooth 47 is spring urged by the tension spring 54 sothat it enters the next slot 48 and this positions the disc 10 such thatthe next peripheral portion to be notched by the punch 15 and die 13 isproperly aligned between the punch and die.

When the disc 10 is held in an angularly fixed position about its ownaxis 29 and with its peripheral portion supported by the die supportingsurface 16 and held on the die supporting surface 16 by means of the twosurfaces 28 on the disc positioning members 26 and 27, vertical downwardmovement of the punch 15, when sufiicient force is applied to the punch15, causes a slug 55 to be punched out of the disc to thereby form thenotch 12 in the periphery of the disc. The base plate 24 has an opening56 therein and the slug 55, when punched out of the disc 10, dropsthrough the opening 56. It is to be borne in mind that the presentfixture is adapted to angle notch steel earth cutting discs having athickness of the order of between one-eighth and one-half inch.Accordingly, the pressure required to move the punch through the disc 10is of the order of upwards of 15 tons depending upon the thickness ofthe disc 10 and the size of the notch 12 to be formed therein. Due tothe fact that the punch 15 passes through the disc 10 at an acute angle,the resistance of the disc to being punched causes a lateral componentof force to be applied to the punch 15, which tends to move it to theright (as viewed in Fig. 1). Inasmuch as the punch 15 abuts the reactionguide member 14, lateral horizontal movement of the punch is prevented.It will be noted that the base plate 24 is provided with a recess 57having a shoulder 58 against which the reaction guide member 14 isseated in order to insure that the reaction guide member 14 itself willnot also be moved due to the lateral force acting upon the punch 15.Since the punch 15 strikes the disc 10 at an acute angle there is also acomponent of force acting toward the left on the die 13 and the die 13is also set into a recess 59 in the base plate 24 and abuts a shoulder60 so as to maintain the die 13 fixed with respect to the base plate 24.

Proceeding now with a description of the operation of the present anglenotching fixture, the peripheral portion of the disc 10 positionedbetween the punch 15 and die 13 lies at an acute angle with respect to aline of reciprocation of the punch 15, indicated by the dotted line 61.This acute angle is shown in Fig. 5A as being approximately equal to 35degrees. It will, of course, be understood, however, that the magnitudeof the acute angle between the disc 10 and the line of reciprocation 61of the punch 15 will depend upon the degree of bevel or sharpnessdesired to be imparted to the notch 12. A smaller angle between the discsurface and the line of reciprocation 61 will cause a sharper cuttingedge to be formed and a greater angle will cause a duller or more bluntcutting edge to be formed.

When the disc 10 is positioned between the punch 15 and the die 13 andthe punch 15 is moved downwardly to the point where it just engages theupper surface of the disc 10, the compression and shearing edges 23a and2322 respectively make line contact with the upper surface of the disc,the edges 23b line contacting the tapered portion 20 of the discperiphery and the edge 23:: line contacting the untapered portion of thedisc. At this same time the combined shearing, back-up and compressionedge 18 on the die 13 also makes line contact with the under surface ofthe disc 1.0.

Upon initial movement of the punch 15 downwardly into the disc 10 untilit reaches approximately the position shown in Fig. 5B or 6B metalfailure of the upper portion of the disc 10 occurs along a compressionsurface 62 which is complementary to the cylindrical surface 19 of thepunch 15. At the same time metal failure of the lower portion of thedisc 10 occurs along a compression surface 63 which is complementary tothe cylindrical surface 17 on the die 13.

Further downward movement of the punch 15 beyond the position thereofshown in Figs. 5B and 68 causes metal failure along a shear surface 64thereby completely severing the slug 55 from the remainder of the disc10. The slug 55 drops out through the opening 56 in the base plate 24and the punch 15 is withdrawn upwardly. The shear surface 64 is acontinuously curved surface which intersects the compression surface 62and which passes through each point on the lower surface of the disc 10that is line contacted by the shearing, backup and compression edge 18.

Inasmuch as the surface 19 on the punch 15 and the surface 17 on the die13 are both cylindrical, the general contour of the periphery of thenotch 12 defined by the compression surface 62 and the shear surface 64is elliptical. The compression surface 62 is substantially complementaryto the cylindrical surface 19 of the punch 15 and therefore it is asemi-cylindrical surface intersecting the upper surface 65 of the discat an angle of approximately 145 degrees, which is the complement of theangle between the disc 10 and the line of reciprocation of the punch 15.As will be apparent from Figs. 78, C, D and E, the angle of intersectionbetween the compression surface 62 and the upper surface 65 of the disc10 decreases from an obtuse angle of approximately 145 degrees at themid-point or radially deepest point of the periphery of the notch 12(represented by the sectional view shown in Fig. 7B and approaches anangle of slightly greater than 90 degrees at the intersection of thecompression surface 62 with the periphery of the disc 10.

The shear surface 64 is a semi-frusto-conical surface rather than a truesemi-cylindrical surface by reason of the fact that a certain amount ofclearance between the punch surface 19 and the die surface 17 isnecessary. The shear surface 64 therefore converges with or intersectsthe lower surface 66 of the disc 10 at a variable acute angle in orderto provide a cutting edge 67. The cutting edge 67, as is apparent fromFigs. 7BE, is sharpest in the radially deepest portion of the notch 12and, becomes duller proceeding toward the terminals (indicated byreference numerals 68) of the notch 12 where the notch defining surfaces62 and 64 intersect the disc periphery. Since it is contemplated thatthe disc 10 will be utilized as an earth-cutting disc primarily, it isnot essential that the periphery of the disc be keen to the point ofhaving a razor-like cutting edge, it only being necessary that theperiphery of the disc 10 be sufficiently sharp to cut through the earthwhich it is desired to work up. Rather than having a keen cutting edgeat the periphery of the disc 10 it is more important that there besufficient thickness of the disc at the periphery so that strength willnot be sacrificed. Consequently, by providing the notch 12 with aperipheral cutting edge that is sharpest in its medial or centralportion and progressively becomes duller at its terminal portions, theelliptically curved cutting edge is sufficiently sharp for working upthe soil and is sufiiciently thick to provide the necessary strength atthe edge of the disc 10.

It has already been pointed out how the edges 18 and 23 on the die 13and punch 15, respectively, function initially to cause metal failure ofthe disc 10 by compression and subsequently to cause metal failure ofthe disc 10 by shear, upon movement of the punch 15 through the disc 10,and it should here be noted that the edge 18 on the die 13 also performsanother very important function. This function of the combined shearing,back-up and compression edge 18 is that it functions to back up the disc10 upon passage of the punch 15 therethrough in order to insure that aclean shear, such as will provide a smooth and continuously curvedsheared surface 64, will always be effected. Due to the continuous linecontact between the shearing, back-up and compression edge 18 and theunder surface 65 of the disc 10, there is no tendency of the disc 10 tobreak raggedly upon passage of the punch 15 therethrough. When metalfailure is sought to be effected through sheet metal, along a surfacethat makes an acute angle with one surface of the sheet, a distinctproblem is encountered which arises from the fact that metal failure issought to be produced along a surface wider than the thickness of themetal. The natural tendency is for the metal to break along a surfacesubstantially at right angles to the sides of the sheet and in thepresent application such a result is entirely undesirable. By providingthe combined shearing, back-up and compression edge 18 the metalimmediately surrounding the periphery of the notch to be subsequentlyformed is backed up and prevented from yielding, and consequentlybreakage of the metal at the notched periphery along a surface whichmight tend to make a right angle with one of the sides of the disc 10,is rendered substantially impossible.

Another problem encountered in angle notching sheet metal at theperiphery thereof, is that problem resulting from the tendency of thepunch to slip or be forced in a horizontal direction away from the metalbeing punched. When this is allowed to take place the compressionsurface which corresponds to the compression surface 62 in the disc 10is not a surface that is truly complementary to the punch surface 19,but instead, is very likely to be an uneven surface more nearly parallelto the sides of the disc. The back-up guide member 14, by preventing ahorizontal shift of the punch 15 during passage of the punch through thedisc 10, serves to insure that the compression surface 62 will beprecisely formed and complementary to the cylindrical surface 19 of thepunch 15.

The present invention therefore discloses a high carbon steel dischaving a tapered periphery and having its periphery angle notched toprovide a cutting edge, of sufiicient keenness to enable the disc to cutearth when it is utilized in an earth-working implement. Further, thepresent invention discloses a fixture and method for providing thenotches in the periphery of a high carbon steel earth-cutting discwherein the notches are defined by a generally elliptical crescentshaped sheared surface which intersects one side of the disc at an acuteangle to thereby provide a cutting edge around the periphery of thenotch. Further, the use of a semi-cylindrical punch for providing thenotches, in a manner such that the punch intersects the taperedperiphery of the disc, is particularly advantageous in that the shearedsurface formed by such a punch intersects one side of the disc at arather blunt angle at the periphery of the disc to thereby still retainsufiicient disc thickness as will afford the necessary strength of thedisc at the notch terminals.

The present invention therefore provides an improved earth-cutting discand an improved method and fixture for forming scalloped cutting edgesin the periphery of such a disc without utilizing a grinding operationto sharpen the cutting edges after the disc is peripherally punched toform the scalloped periphery thereof. The combination of parts in thenotching fixture comprising the combined shearing, back-up andcompression edge on the die, the complementary compression and shearingsurface on the punch, the back-up reaction guide member for the punchand the means for supporting the tapered periphery of the tempered sheetmetal disc at an angle to the path of travel of the punch are allcritical to the formation of the new and improved earthcutting disc.

Although specific values have been utilized in describing the presentinvention, in particular with respect to the angle between the sides ofthe disc and the line of reciprocation of the punch and also withrespect to the hardness of the steel of which the disc is made, it is tobe borne in mind that these values have been found to be satisfactoryand have been set forth specifically to illustrate a specific example ofthe form of disc disclosed herein. It is contemplated that numerouschanges may be made in this respect particularly and in other respectswithout departing from the spirit or scope of the invention.

What is claimed is:

1. A hard sheet metal object having a tapered peripheral portion andhaving a recess in its peripheral portion, said recess being defined bya substantially contint ously curved sheared surface meeting one side ofthe object at a variable acute angle to thereby form a cutting edge,said acute angle having the smallest value at the radially deepest pointon the cutting edge and gradually increasing in value and approaching aright angle at the ends of said curved sheared surface.

2. A high carbon steel earth cutting disc having opposed sides one ofwhich is substantially uniformly tapered around its periphery, andhaving a sheared open mouthed recess formed in its peripheral portion,said recess having a radial depth greater than the radial width of thetaper on said one side of the disc and being defined by a substantiallycontinuously curved surface meeting one of the sides of the disc at avariable acute angle to thereby form a cutting edge, said acute anglehaving the smallest value at the radially deepest point on the cuttingedge and gradually increasing and approaching a right angle at the endsof said curved sheared surface.

3. A high carbon steel concave earth cutting disc having one sidethereof peripherally tapered to provide a relatively blunt cutting edgeon the periphery of the disc and having a notch formed in its peripheralportion, said notch being defined by a sheared surface that intersectsthe other side of the disc at a relatively small acute angle in thecentral portions of the notch and at a relatively large acute angle atthe terminal portions of the notch so as to provide a relatively sharpercutting edge around the notch and still maintain sufficient discthickness at the junctures of the notch and the tapered periphery of thedisc as will not weaken the disc at said junctures.

4. A tempered sheet metal earth cutting disc the diameter of which isgreater than 20 times the thickness of the disc, said disc having agenerally semi-elliptically shaped notch in its peripheral portion, saidnotch being defined by a pair of intersecting surfaces each of whichintersects the periphery of the disc, one of said surfaces comprising apunch compressed surface meeting one side of the disc at an obtuse angleand the other of said surfaces comprising a punch sheared surfacemeeting the other side of said disc at a variable angle sufficientlyacute to provide a cutting edge.

5. A tempered sheet metal earth cutting disc having a peripheral portionformed with an open continuously curved recess therein, said recessbeing defined by a pair of intersecting punch compressed and punchsheared surfaces, the punch compressed surface comprising a surfaceintersecting one side of the disc at a variable obtuse angle of theorder of 140 to 150 in the medial portions of the punch compressedsurface and gradually decreasing and approaching a right angle at theterminal portions thereof, and the punch sheared. surface meeting theother side of the disc at an acute angle of the order of 35 to 45 in themedial portions thereof and gradually increasing and approaching a rightangle at the terminal portions thereof to provide a cutting edge for therecess.

6. In a metal earth cutting disc having a tapered periphery, a curvedrecess in said periphery defined by a generally crescent shaped shearedsurface, said surface converging with one side of said disc at an anglethat varies proceeding inwardly from the periphery of said disc fromsubstantially a right angle at the relatively thin periphery of the discto a relatively sharply acute angle at the radially inner portion of theconvergence to define with said one side an earth cutting edge.

References Cited in the file of this patent UNITED STATES PATENTS

